1. Field of the Invention
This invention relates to shaping heat softened glass sheets, and in particular, to shaping pairs of glass sheets to a curved configuration by a combination of preliminary gravity sag bending on an outline mold, and final press bending between an upper ring press and a vertically aligned, full surface lower press face using pressurized gas to supplement shaping.
2A. Technical Consideration
One common technique for shaping a glass sheet is to support the sheet on an outline bending mold having a shaping rail with an upper surface having elevational contours corresponding to the final desired shape of the glass sheet. The glass sheet is heated to its heat softened temperature and sagged by gravity to assume the desired configuration. This technique is particularly well suited for simultaneously shaping two sheets of glass, or doublets, that will be used as the inner and outer plies of conventional laminated glass, for example a windshield.
As glass sheet configurations become more complex and include deeper bend sections, the shaping rails may be segmented and made to pivot from an open, rigid sheet supporting position to a closed, heat softened glass sheet supporting position. In the closed position, the shaping rails assume the desired elevational contours of the glass sheet to be shaped slightly inboard of its perimeter.
In addition, pressing molds may be used to shape glass doublets to complex and complicated configurations by pressing the glass sheets between a pair of aligned, full surface press faces. When pressing molds are used in conjunction with an outline mold, the lower mold generally moves upward through the rail of the outline mold, lifting the glass sheet off of the outline mold and presses it against a complementing upper mold. However, when the surface of heat softened glass is contacted by a pressing surface, there is a risk of marking the contacted surface.
It would be advantageous to provide a bending arrangement wherein glass sheets can be preliminarily shaped on an outline bending mold and then pressed between a pair of bending molds to impart a final configuration while minimizing the surface contact between glass sheets and the press face surfaces.
2B. Patents of Interest
U.S. Pat. No. 2,131,873 to Goodwillie shapes one or a pair of glass sheets by supporting the glass sheets on an upwardly facing concave shaping surface of a solid lower mold, allowing the glass sheets to sag by gravity to conform to the shaping surface, and pressing the sheets between the lower mold and an upper solid mold having a complementary convex shaping surface. The glass sheets remain on the lower mold throughout the sagging and press bending operation.
U.S. Pat. No. 2,570,309 to Black sag bends a glass sheet by heating it while supporting the sheet on an outline ring-type mold to conform to the mold by gravity sagging. The gravity sagged glass sheet is then lifted on a lower solid pressing mold of concave elevation into pressing engagement against an upper solid pressing mold of complementary shape. The bent glass sheet is returned to the outline ring-type mold to support the bent glass sheet during quenching.
U.S. Pat. Nos. 3,068,672 to Black; 3,408,173 to Leflet; 3,976,462 to Sutara; and 4,597,789 to Reese disclose outline metal molds for shaping a glass sheet of non-rectangular outline to a nonuniform shape by gravity sag bending. Black, Sutara and Reese each further disclose a sectionalized outline metal mold for the gravity sag bending.
U.S. Pat. No. 3,208,839 to Nordberg press bends as many as three glass sheets to conforming shapes simultaneously using press bending techniques exclusively for the shaping process.
U.S. Pat. No. 3,582,454 to Giffen teaches a glass article forming and trimming apparatus. Layered glass is clamped between a pair of molds and a blow head admits fluid into the cavity between the molds to force the glass into conformity with the surface of one of the mold surfaces. A trimmer penetrates the periphery of the glass to cut the glass to shape.
U.S. Pat. Nos. 4,260,408, 4,260,409, 4,265,650 and 4,290,796 to Reese et al. and 4,272,275 to Reese disclose the simultaneous shaping of a pair of glass sheets having a non-rectangular outline of nonuniform curvature by combination of gravity sag bending and press bending to a complicated shape using full surface, vertically aligned press faces.
U.S. Pat. No. 4,274,858 to Claassen et al. teaches a vertical press bending operation wherein glass is pressed between an adjustable, peripheral shaping member and a full surface press face. The adjustable member is adjustably secured to a rigid plate to adjust its shape.
U.S. Pat. No. 4,305,746 to Hagedorn et al. teaches the shaping of a glass sheet by using a lower press ring to lift a glass sheet against an upper mold face. Shaping pads within the outline of the ring lift the central portion of the glass sheet and press it against the upper shaping mold.